Of all the world’s mountain ranges, the Alps are unique in one particular regard: their outer perimeter is specifically defined by an international treaty, which is based on key principles of sustainable development. In 1991, most of the Alpine States adopted the Convention on the Protection of the Alps (usually known as the Alpine Convention); by 1995, all the signatories – Austria, the European Community, France, Germany, Italy, Liechtenstein, Monaco, Slovenia and Switzerland – had ratified it. Article 1 of the Convention begins by defining the Alps according to a map which is annexed to the Convention (Figure 1). Notably, this map includes the Principality of Monaco, but not a corridor to its north which includes major transport infrastructure. This shows the importance of political processes in defining mountain regions and, as discussed below and in Part 3, of transport and accessibility through and around the Alps as a key issue for the Alps’, and Europe’s, sustainable development.